若tanα=
|
若tanα=
，α是第三象限的角，则由同角三角函数的基本关系可得 sin2α+cos2α=1，3 4
=sinα cosα
，3 4
且sinα＜0，cosα＜0．
解得 sinα=-
，cosα=-3 5
．4 5
∴sin（α+
）=sinα cosπ 4
+cosαsinπ 4
=-π 4
•3 5
-2 2
•4 5
=-2 2
，7 2 10
故选 A．
| 阅读理解。 | |
| Come and see the Indian elephants and tigers from America. The koalas are waiting to meet you, and the monkeys from Thailand are waiting to throw things at you. The cute dogs from Australia are waiting to laugh at you, and the giraffes from Zambia are-waiting to look down on you.
| |
| 1. How many kinds of animals are talked about in the poster (海报)? | |
| A. 4 B. 5 C. 6 D. 7 | |
| 2. Mr. and Mrs. Brown Will take their twins aged 6 to the park. How much will the tickets be together (总共)? | |
| A. $6 B. $12 C. $18 D. $24 | |
| 3. Visitors can do the following things EXCEPT (除了) _________. | |
| A. giving some food to the tigers B. watching the elephants dancing C. laughing at the dogs from Australia D. taking some photos | |
| 4. From the passage we can know the animal "giraffe" is _________. | |
| A. long B. fat C. tall D. strong | |
| 5. The poster may be made (制作) just _________. | |
| A. on New Year's Day B. on Christmas Day C. after Children's Day D. before Children's Day |